This invention relates to a container for housing a photo mask for use in fabrication of an electronic device or a mask blank for use in fabrication of the photo mask and to a method of housing the photo mask or the mask blank.
This invention also relates to a method of housing a mask blank with a resist film, which is for producing a photo mask for use in manufacture of an electronic device.
This invention also relates to a method of treating a housing member for housing a mask blank with a resist film, which is for producing a photo mask for use in manufacture of an electronic device.
Following rapid development of the IT (Information Technology) industry, a recent electronic device, in particular, a semiconductor device, a color filter or a TFT (Thin Film Transistor) element for a LCD (Liquid Crystal Display) monitor, or the like is required to have a finer structure. One of techniques supporting fine process technology for such a finer structure is a lithography technique using a photo mask called a transfer mask. In the lithography technique, a silicon wafer with a resist film is exposed through the transfer mask to an electromagnetic wave from an exposure light source so that a fine pattern is formed on the silicon wafer. Generally, the transfer mask is produced by preparing a mask blank comprising a light transparent substrate and a light shielding film formed thereon and forming an original pattern on the mask blank by the use of the lithography technique. If foreign matters such as particles are present on a surface of the mask blank, this may result in occurrence of a defect of the pattern formed on the silicon wafer. Therefore, the mask blank must be stored in a clean condition so that no foreign matters are adhered or attached to the surface of the mask blank.
For example, as a conventional container for housing, storing, and carrying a mask blank, a mask carrying case is disclosed in Japanese Patent Application Publication (JP-A) No. 2001-154341.
Specifically, the conventional container for housing and storing a mask blank comprises an inner case called a carrier, an outer case (container body), and a cap. Several to several tens of mask blanks are held in the inner case in parallel to one another. The inner case with the mask blanks held therein is received in the outer case. Then, the cap is put on the outer case. In this manner, the mask blanks are housed in the container. An adhesive tape is attached to a joint portion between the outer case and the cap to hermetically seal the container and to prevent entry of ambient air and foreign matters. In most cases, the container is made of a resin material.
Following recent improvement in performance of the electronic device, the original pattern formed on the transfer mask is also required to be finer. In order to form such a finer pattern, the mask blank must have an extremely high cleanliness. Therefore, it is necessary to maintain as high cleanliness as possible, in particular, during storage of the mask blank by minimizing adhesion of foreign matters to the mask blank. Among others, in case of a mask blank having a resist film formed on a surface thereof, the foreign matters once adhered to the surface are difficult to be removed. Further, cleaning is impossible at this stage. Therefore, patterning is carried out with the foreign matters adhered to the surface. This results in occurrence of a pattern defect.
In the meanwhile, attention is recently directed to a chemically amplified resist as a resist for a photo mask. For example, the chemically amplified resist is described in Japanese Patent Application Publication (JP-A) No. 2000-66380. The chemically amplified resist is superior in characteristics, such as sensitivity and contrast, than a photo resist which has been used so far and is therefore advantageous in forming a finer pattern. However, it is pointed out that the chemically amplified resist is susceptible to an influence of a contaminant of a chemical component because of its reaction mechanism. Specifically, in presence of a contaminant of a certain chemical component, a function of a substance serving as a catalyst for chemical amplification may be suppressed or inhibited (for example, deactivated) so that a desired performance can not be obtained.
The chemically amplified resist contains either a high-molecular-weight compound having a resist function (positive type) or a low-molecular-weight compound which produces a high-molecular-weight compound by a cross-linking reaction or the like (negative type), and a catalytic substance. By irradiating the chemically amplified resist with energy radiation such as electron wave or electromagnetic wave, the catalytic substance contained therein is exposed to produce an acidic catalytic substance in the resist. The acidic catalytic substance has a catalytic function for a chemical reaction (chemical amplification) of making the high-molecular-weight compound soluble to a liquid developer or producing a high-molecular-weight compound and making the high-molecular-weight compound insoluble to the liquid developer. However, it is pointed out that the chemically amplified resist is susceptible to an influence of a contaminant of a basic chemical substance because of its reaction mechanism. Specifically, in presence of a contaminant of a certain basic chemical substance, for example, ammonia or amine, production of the acidic catalytic substance serving as a catalyst for chemical amplification may be inhibited or a function of the acidic catalytic substance produced as mentioned above may be suppressed or inhibited (for example, deactivated) so that a desired performance can not be obtained.
In view of the above, in case of the mask blank with a chemically amplified resist film formed thereon, it is necessary not only to eliminate foreign matters such as particles but also to eliminate an influence of a contaminant of a chemical substance. Therefore, the mask blank with a chemically amplified resist film must be stored in an especially clean atmosphere.
In the conventional container for a mask blank, the joint portion between the outer case and the cap is hermetically sealed by the adhesive tape. However, this requires double efforts of adhering the tape upon housing and packaging the mask blank and removing the tape upon opening the container. In addition, a sealed state is incomplete or insufficient. Specifically, the adhesive tape generally used has some breathability. Depending upon temperature variation of the atmosphere in which the container is stored, internal air within the container may be expanded or contracted. In this event, airflow between the ambient air and the internal air occurs through the joint portion to which the tape is adhered. Sometimes, pressure of the atmosphere may be varied, for example, in case where the mask blank is transported on board an aircraft. In case of transportation on board the airplane, variation in pressure is considerably large. In this case also, airflow occurs between the ambient air and the internal air. Therefore, even if the mask blank is housed and packaged into the container in a clean atmosphere such as a clean room, the ambient air may enter into the container with lapse of time depending upon a storage atmosphere after packaging. In this event, the interior of the container may be contaminated by a certain component contained in the ambient air.
Further, even if the container is made of a material, such as plastic, which hardly releases any chemical component or the like, a chemical component used in a base member of the adhesive tape or an adhesive agent may enter into the container with lapse of time to cause contamination. In particular, upon occurrence of variation in atmosphere, such as temperature change or pressure change mentioned above, contamination by the chemical component released from the tape may be accelerated.
In particular, in case of the mask blank with the chemically amplified resist film mentioned above, contamination by the chemical component or the like causes a crucial defect and must be completely avoided.
At a glance, it seems possible, by housing and packaging the mask blank into the container within the clean room or the like and sealing the joint portion between the outer case and the cap by the adhesive tape, to prevent entry of the ambient air and store the mask blank in a clean atmosphere. Actually, however, it is difficult to avoid contamination by the entry of the ambient air or contamination by the chemical component of the adhesive tape.
According to the study by the present inventor, it has been found out that, even if contamination by the basic chemical substance is avoided, a stable resist function is not always obtained and a desired resist pattern is not always formed. Specifically, it has been found out that, even if a factor causing the basic substance such as amine to be generated during a manufacturing process of the mask blank having the chemically amplified resist film is thoroughly investigated and eliminated and, further, close attention is paid to an environment of housing and packaging the mask blank, there still arises a problem of fluctuation in accuracy of the resist pattern formed on the mask blank.
In order to eliminate the influence of the contaminant of the basic chemical substance, the mask blank with the chemically amplified resist film may be housed and packaged in an atmosphere cleaned by the use of a chemical filter. Even in this event, the mask blank housed in the container may be contaminated by a basic substance released as an outgas from the container during subsequent storage. In particular, depending upon the temperature change or the pressure change of the ambient air during storage, release of an outgas component may be accelerated. In this case, it is proposed to use a material which releases a small amount of the outgas component with lapse of time. In this approach, however, contamination with lapse of time can not completely be eliminated and the material of the container is restricted.